• Tag : ECMP


Support for Hierarchical Nexthop-groups

Description Nexthop-groups is a routing mechanism where users can configure a set of nexthops by specifying their nexthop addresses and associated encapsulation information in a group. Each nexthop-group is referred to by a unique name and can support a single tunnel type like IP, GRE, MPLS, etc. Static routes that directly resolve through nexthop-groups can be configured. Any traffic destined to an IP address covered by such static routes will then be forwarded via the nexthops specified in the corresponding nexthop-group. Nexthop-groups can be used to achieve Equal-Cost Multi-Path (ECMP) routing by configuring multiple nexthop entries. However, on some platforms,...
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Multicast tree control in multi-tiered fabrics

Description Multipath color is a new multicast multipath mode for controlling PIM RPF selection. In the default multipath deterministic mode, multiple PIM routers with the same set of ECMPs to the source may make a different RPF selection decision. This may result in wasted bandwidth consumption since traffic may be unnecessarily duplicated. In multipath color mode, all PIM routers with the same set of ECMPs to the source make the same RPF selection decision (per source-group). Traffic is load balanced across ECMPs by source-group. Upstream PIM routers advertise a multipath color value in the PIM Hello message that downstream PIM...
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ECMP Hash Visibility

Description ECMP Hash visibility CLI determines the output interface for an ECMP set based on the flow parameters supplied by the user. Ingress interface, source IP address, destination IP address and IP protocol are the required parameters. L4 source and destination ports and VLAN identifier are optional, but should be specified if the packet has them. The command also supports tunnel encapsulated traffic calculation (IP-in-IP, GRE) and provides optional fields for these. 7050(config)# show load-balance destination ingress-interface <interface> { src-ipv4-address <ipv4-address> dst-ipv4-address <ipv4-address> | src-ipv6-address <ipv6-address> dst-ipv6-address <ipv6-address> } ip-protocol <protocol> { { inner src-ipv4-address <ipv4-address> inner dst-ipv4-address <ipv4-address> inner...
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Resilient ECMP deduping

Description Routes covered by a resilient equal-cost multi-path (RECMP) prefix are types of routes that make use of hardware tables dedicated for equal-cost multi-path (ECMP) routing. Resilient ECMP deduping is a new feature wherein the switch will reactively attempt to reduce the number of ECMP hardware table entries allocated by forcing routes that share the same set of next hops but point to different hardware table entries to point to the same hardware table entry when hardware resource utilization is high. Forcing RECMP routes to change the hardware table entry that they point to may potentially cause a traffic flow...
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Support for ECMP routes in RIP

Description This feature adds the support for learning multiple equal cost routes for a destination in the RIP protocol. This increases the robustness as well as enables the router to load balance the traffic through different paths. This feature will only support enabling or disabling of the ECMP and users will not have an option to control the maximum number of next hops in an ECMP route. By default, ECMP is disabled. The feature is supported in both single-agent as well as multi-agent routing protocol models. Platform compatibility This feature is provided on all platforms. Configuration The following CLI command...
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ECMP head

Hello, In a switch configured for ECMP, what is the difference between ECMP head and ECMP paths? sh ip bgp * >Ec … * ec …

MPLS static tunnel ECMP

Description EOS version 4.24.1F introduces support for specifying multiple vias to form ECMP in MPLS static tunnels. A new configuration mode for an MPLS static tunnel is introduced, where it is possible to enter one or multiple vias for said tunnel. Platform compatibility This is largely a platform-independent feature and therefore will work on all Arista platforms which meet the following requirements: Running a control plane in multi-agent mode. Using a data plane which supports MPLS forwarding. See section Limitations of MPLS encapsulation TOI: https://eos.arista.com/eos-4-15-0f/mpls-encapsulation/ Configuration For CLI configuration details and legacy (“single line”) MPLS static tunnel configuration, please refer...
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BGP best paths and best ECMP paths counters

Description It is often useful to know on a per AFI/SAFI basis, the number of paths that have been selected from a peer as best paths. For example, we may have configured a policy to ensure that paths from a particular peer are most preferred, and it would be useful to have a quick way of confirming this. Similarly, we may need to divert traffic away from a peer, and we may use a policy to reduce the preference of paths received from the peer to accomplish this. This feature provides an easy way to know the number of paths/prefixes...
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Hardware resource optimization for route programming

Description On network devices, when a route is programmed, a certain portion of hardware resources is allocated and associated with the route. Such resource allocation and association might be sub-optimal or redundant in order to maintain fast convergence when the network is churning. For example, when an “equal-cost multi-path” (ECMP) route is programmed and some of the ECMP links are down, the resources allocated to the route may not be released so that the route can recover quickly (as there is no hardware churning) when those links are up. However, since the hardware resources for routes are limited, maintaining sub-optimal...
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Support to Restrict the Number of Bgp Ecmp Next Hops in Multi-Agent Protocol Model

Description In the ribd routing protocol model, the “maximum-paths … ecmp …” command allows restricting the number of BGP paths and the number of vias in the ECMP FEC respectively. In the multi-agent protocol model, a “maximum-paths” value of greater than 1 enabled the formation of ECMP. However, the number of BGP paths or the number of vias in the FEC were not constrained by the configured value. With the 4.24.0F EOS release, the multi-agent protocol model supports restricting the number of BGP paths and ECMP FEC size based on the BGP configuration. Platform Compatibility Supported on all platforms. Configuration...
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Arista DCS-7280SRAM-48C6-F ECMP Hashing

I have a few questions around ECMP and hashing.I can’t seem to find a straight answer via documentation. – What algorithm does EOS use for BGP ECMP hashing? Is it per flow (source/designation)? – Is there a command to determine which route a source/destination will take?

ECMP Load Balance Profile Support

Description As of 4.22.1F Load Balance Profiles can be used to explicitly configure ECMP Load Balance parameters. In addition, users can choose from up to 8 hash polynomials instead of the usual 3 for ECMP and LAG (see Limitations). Platform compatibility DCS-7280E DCS-7280R DCS-7280R2 DCS-7280R3 DCS-7020R DCS-7500E DCS-7500R DCS-7500R2 DCS-7500R3 DCS-7800R3 Configuration Load Balance Profile mode This feature extends existing Load Balance Profiles configuration (see https://eos.arista.com/eos-4-15-0f/lag-hashing/ for more information on how to configure load-balance profiles). The user can choose to modify the default profile or create a custom one.  To enter the profile mode issue the following commands. Arista(config)#load-balance policies...
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ecmp bgp question

Here my scenario : sw1 sw2 ! ! ebgp ebgp ! ! servers x1 servers x2 Basically I have some servers which peer locally on each arista switchs. All the servers advertise some /32 (via bird), which I want to be equally distributed on each switch. router bgp 49477 router-id graceful-restart restart-time 300 bgp always-compare-med maximum-paths 64 bgp listen range peer-group prdinfcdn remote-as 65042 no bgp bestpath ecmp-fast neighbor ipv4-ibgp peer-group neighbor ipv4-ibgp remote-as 49477 neighbor ipv4-ibgp update-source Loopback0 neighbor ipv4-ibgp additional-paths receive neighbor ipv4-ibgp additional-paths send any neighbor ipv4-ibgp maximum-routes 12000 neighbor prdinfcdn peer-group neighbor prdinfcdn remote-as...
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Exposing ECMP hashing algorithm details

I need to determine the ECMP path (route) to be taken by a specific packet (combination of packet header fields). I use an Arista 7050TX switch with EOS v. 4.18.6M . It seems there is a command in config mode (show load-balance destination ingress-interface {used header fields}) which helps determine the outgoing interface for a specific packet. The Arista blog post however is not publicly visible. Could someone provide a detailed explanation of the command? Alternatively and preferably, I would like to reproduce the hashing algorithm behaviour. My attempts to track that so far bare no results. I can set...
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MLAG ECMP load balance method

Hello, I need a help with proper design. I have a pair 7050X with MLAG configuration. To the downstream devices I have 2 mlag port-channels each contain 2 links. 7050X will provide L3 functionality : gateways and routing.  I would like to enabling ecmp and load-balance the traffic. What will be the best method to choose in this scenario ?   Thank you

Arista 7280QR-C36 Load Balancing Optimization for Dual Homed Systems and Networks

Arista 7280QR-C36  The Arista DCS-7280QR-C36 switch is a purpose built flexible fixed configuration 1RU system capable of supporting a wide range of interface choices. Its designed for the highest performance environments such as IP Storage, Content Delivery Networks, Data Center Interconnect and IP Peering. The 7280QR-C36 is optimized for environments with dual connected nodes such as storage and for spine applications with dual homed leaf switches. This technical application note describes the internal optimized load-balancing mechanism used within the switch and how network architects can best deploy this system to maximize overall system performance. The internal architecture of the DCS-7280QR-C36...
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Load Balancing with ECMP: Hardware Configuration Lookup

Abstract: This publication illustrates a technique which can be used to find exactly how Arista devices program routes to send traffic across multiple available paths. An example will be given on the Arista DCS-7150S-52-CL-R running EOS version 4.14.8M. Initial configuration: As an IGP we are using OSPF with maximum paths feature configured: Arista(config)#router ospf 1 Arista(config-router-ospf)#maximum-paths 32 There are two iBGP peers configured via a peer-group “pg1”: Arista(config)#router bgp 65001 Arista(config-router-bgp)#neighbor pg1 maximum-routes 16000 Arista(config-router-bgp)#neighbor peer-group pg1 Arista(config-router-bgp)#neighbor peer-group pg1 iBGP advertisements: * >    0       100     0       64920 64944...
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ECMP Hash Visibility

Description ECMP Hash visibility CLI determines the output interface for an ECMP set based on the flow parameters supplied by the user. Ingress interface, source IP address, destination IP address and IP protocol are the required parameters. L4 source and destination ports and VLAN identifier are optional, but should be specified if the packet has them.   7050(config)# show load-balance destination ingress-interface <interface> { src-ipv4-address <ipv4-address> dst-ipv4-address <ipv4-address> | src-ipv6-addess <ipv6-address> dst-ipv6-address <ipv6-address> } ip-protocol <protocol> [src-l4-port <port#> dst-l4-port <port#>] [vlan-id <vlan>] Platform Compatibility 7050X 7250X 7300 7050 7010 7368 7060DX4-32 7068PX4-32 Configuration Example 1 Say, the routes programmed in...
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How to test load-balancing feature using ECMP on vEOS

Hi, all I installed vEOS 4.15.2 to test load-balance feature. I can’t find the related commands, such as ‘ip route load-balance’ and ‘port-channel load-balance’. Is it not supported from vEOS version? Please help me~ Thanks,


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